Marketable Investments - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended	12 Months Ended
	Oct. 30, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Auction rate securities par value		$ 80,988,000	$ 80,988,000
ARS [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Auction rate securities par value		11,000,000	11,000,000
Loss realized on ARS	1,900,000	1,900,000	1,900,000
Proceeds from sale of ARS	$ 9,100,000
Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Intervals for each security				7 days
Interest rates on securities ranged			0.10%		0.10%
Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Intervals for each security				35 days
Interest rates on securities ranged			0.40%		0.50%